1. Field of the Invention
The present invention relates to a brazing paste for use in bonding together metal and ceramic. The U.S. application Ser. No. 154,273 filed on Feb. 10, 1988 relates to the present application.
2. Description of the Related Art
A circuit board with a semiconductor device mounted thereon includes, for example, a resin board, metal board or ceramic board. Of these boards, the ceramic board has extensively been used in terms of its excellent heat radiation characteristic, electrical characteristic and overall reliability over those of the other boards. In view of a recent development of ceramics excellent in heat conduction characteristic and heat radiation characteristic, there is a growing demand for ceramic boards.
When metal and ceramic are bonded together, for example, input/output terminal pins are joined to the ceramic circuit board, pin joining spots on the ceramic circuit board are plated with Ni in the prior art technique to provide pads of high wettability to a metal brazing material and then the terminal pin is brazed or soldered to the pad. However, this method requires a wider pad area for enhancing a strength of bond to the pin, making it difficult to make a bond of the terminal pin to the pad in high density. Some of the ceramic for use for the board reveal a poor wettability to a brazing or soldering melt, failing to make a firm bond to the terminal pin.
In view of the above situations a new method has been developed in which the terminal pin is joined to the ceramic circuit board in a vacuum furnace with the use of an active metal brazing material containing Ti, Zr, etc. However, this method cannot attain a high-quantity production for a practical use.
In order to circumvent the disadvantage involved in the aforementioned method using the vacuum furnace a method has been conceived which employs an active metal-added paste under an N.sub.2 atmosphere. If use is made of such a paste, it is scattered around upon being heated, degassed and cured, causing a degradation in a bond surface uniformity and hence in an outer appearance. A poor electrical characteristic, i.e. a drop in insulation resistance sometimes occurs in the body.